I managed to pick it up in about 2000 from a guy that had collected models since the mid 60's and this was one of them he hadn't put together. All of the pieces are there, but not everything is still connected to the trees. I'll probably just leave it like this. Are there currently any '67 or '68 plastic models being produced?

You can find a 1967 resin conversion kit. They show up on ebay from time to time usually in the $40 range plus shipping. You will need to use one of the newer 1969 kits for some of the parts to complete the model.